From the Guidelines
Cortisol blood tests cannot definitively tell you how stressed you are due to the natural fluctuations in cortisol levels throughout the day and the complexity of the stress response. A single cortisol measurement offers limited insight because cortisol levels follow a circadian rhythm with highest levels typically in the morning and lowest at night, as noted in a study published in 2020 1. This natural variation, combined with the fact that stress involves multiple physiological and psychological factors, means that a single biomarker like cortisol cannot capture the full picture of stress.
Key Points to Consider
- Cortisol levels naturally fluctuate throughout the day, making a single measurement less informative
- Stress is a complex phenomenon that cannot be fully assessed with a single biomarker
- Multiple cortisol measurements or specialized tests may provide more comprehensive information about stress levels
- Clinical evaluation, psychological assessments, and consideration of symptoms are crucial for a complete understanding of an individual's stress levels For more comprehensive stress assessment, multiple cortisol measurements throughout the day (known as a diurnal cortisol profile) or specialized tests like the cortisol awakening response may be more informative, as they can account for the natural fluctuations in cortisol levels and provide a more detailed picture of the body's stress response. These tests, however, should be interpreted by healthcare professionals who can consider other factors like medical conditions, medications, and individual variations, as highlighted in guidelines from 2017 1. Ultimately, cortisol testing is most useful when combined with clinical evaluation, psychological assessments, and consideration of symptoms, as the body's stress response involves many systems beyond just cortisol, including other hormones, neurotransmitters, and immune factors.
From the Research
Cortisol Measurement in Blood Tests
- Cortisol levels in a blood test can indicate the presence of certain medical conditions, such as Cushing syndrome, which is characterized by a prolonged increase in plasma cortisol levels 2.
- Serum cortisol measurement is a useful tool in the biochemical evaluation of adrenocortical function, and it can be measured in blood, urine, saliva, and other biological fluids and tissues 3.
- A single measurement of serum cortisol can be used to investigate suspected adrenal insufficiency, with morning and afternoon thresholds identified to determine which individuals require dynamic testing 4.
Factors Influencing Cortisol Measurements
- Various factors can influence the adrenocorticotropin test, including contemporary cortisol assays, body composition, and oral contraceptive agents 5.
- Oral administration of certain medications, such as oxazepam, can suppress plasma cortisol levels for a period of time 6.
- The normal response to an adrenocorticotropin test is assay specific, and both total cortisol and calculated free cortisol can be affected by certain factors, such as oral contraceptive use 5.
Limitations of Cortisol Measurements
- Cortisol levels in a blood test may not directly indicate stress levels, as cortisol can be influenced by various factors, including medical conditions and medications.
- The measurement of cortisol in blood tests is typically used to diagnose and monitor certain medical conditions, rather than to assess stress levels 2, 3, 4, 5, 6.